The invention relates to a machine for the non-circular machining of workpieces comprising a machine frame, a workpiece spindle held on the machine frame for receiving a workpiece, a C-axis sensor for determining the rotary positions of the workpiece spindle, a Z-slide arranged on the machine frame for displacement in the Z-direction parallel to the workpiece spindle and having a Z-axis drive, a Z-axis sensor for determining the position of the Z-slide, an X-axis drive arranged on the Z-slide for advancing a tool in the X-direction towards the workpiece, an X-axis sensor for determining the position of the tool, and a control device for activating the X-axis drive in dependence upon the values measured by the C-axis sensor, the Z-axis sensor and the X-axis sensor such that a non-circular workpiece shape predetermined for the control device is produced during the machining.
Such a machine is known, for example, from EP-A-0 201 230. This publication discloses a control device comprising a numerical control system in which an analog closed-loop control system for activating the C-axis drive is integrated. The numerical control system predetermines for the analog closed-loop control system the sequence of the data representing the non-circular shape of the workpiece in digital form so that the analog closed-loop control system only links the values of the X-axis sensor, the C-axis sensor and the Z-axis sensor.
Such a "mixed" control system brings problems and is subject to limitations with respect to its accuracy and the adaptability of its control characteristics to an X-axis drive.
The object underlying the invention is, therefore, to so improve a machine of the generic kind that it operates quickly and reliably and allows optimum adaptation to the chosen X-axis drive.